1. Field of the Invention
The present invention relates generally to an inspection system, and in particular to an inspection system for detecting explosives and other contraband using an inductive sensor employing anti-symmetric current branches.
2. Discussion of the Related Art
Presently, the detection of explosives and other contraband may be accomplished using inspection and detection systems implementing a variety of different technologies including nuclear quadrupolar resonant (NQR), nuclear magnetic resonance (NMR), metal detection, and the like. In prior NQR testing systems, for example, a sample is placed within a radio frequency (RF) coil and is typically irradiated with pulses or sequences of pulses of electromagnetic radiation having a frequency which is at or very close to one or more resonance frequencies of the quadrupolar nuclei in a substance which is to be detected. If the substance is present, the irradiating energy will generate a precessing magnetization which can induce voltage signals in a detection coil adjacent the sample at the resonance frequency, and which can be detected as a free induction decay during a decay period after each pulse, or as an echo after two or more pulses.
Conventional inspection systems utilizing inductive sensors have employed various techniques for shielding the system from external noise. One technique is to completely enclose the sensor in an electrically connected and grounded box. Another technique which is commonly used for NQR sensors, is to position the sensor within an enclosure having a wave-guide tunnel positioned at the entrance and exit to the inspection system. While such configurations have enjoyed considerable success in many respects, their use has been limited for inspecting humans since some people are wary or uncomfortable about having to walk and stand in confined spaces.